1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus and, more particularly, to an exposure apparatus for manufacturing semiconductors comprising an exposure optical system, stages for carrying a wafer, movement means for moving the stages relative to the exposure optical system, and measurement means for measuring the positions of the stages.
2. Description of the Related Art
FIG. 4 is an elevation of the configuration of an exposure apparatus of this type. In FIG. 4, the exposure apparatus comprises an illumination section 1 for illuminating a reticle pattern; a reticle 2 having the pattern to be transferred; a projection lens 3 for projecting the pattern formed on the reticle onto a wafer; a lens-barrel support member 4 for supporting the projection lens 3; a finely adjustable stage 5 for placing the wafer (not shown in the figure), the stage having a function of moving in the Z and .theta. directions and tilting in directions about the X-Y plane; an X stage 6 for carrying the finely adjustable stage 5 and moving in the X direction; a Y stage 7 for moving in the Y direction; a stage base 8 for supporting the X and Y stages 6 and 7; a surface plate 9 for supporting and securing the stage base 8 placed thereon, the plate being combined with the lens-barrel support member 4; air mounts 10 placed at four locations for supporting the surface plate 9; laser interferometers 11a and 11b (not shown) for measuring the relative position of the projection lens 3 and the finely adjustable stage 5 in the X direction and the Y direction; mirrors 12a and 12b for reflecting laser light emitted from the laser interferometers 11a and 11b; and a light emitting section 13a and light receiving section 13b of a focus detection block for measuring the focus point of the projection lens 3.
The finely adjustable stage 5 is configured as shown in FIGS. 5(a) and 5(b) (sectional view taken on the X-Z plane). There are shown a finely adjustable top plate 16, a guide mechanism 17 for guiding the finely adjustable top plate 16 in the Z direction, a drive mechanism 18 for driving the finely adjustable top plate 16 in the Z direction, such as a stepper motor, and a pin or pins 14 secured on the X stage 6 for transferring a wafer 15.
When a pattern is formed on the wafer 15 with exposure, as shown in FIG. 5(a), the finely adjustable top plate 16 is driven such that the upper end of the finely adjustable top plate 16 is positioned higher than that of the pins 14. The wafer 15 is exposed to light while it is being held on the finely adjustable top plate 16. When the wafer 15 is transferred to a hand (not shown in the figure), the finely adjustable top plate 16 is driven such that the upper end of the finely adjustable top plate 16 is positioned lower than that of the pins 14, as shown in FIG. 5(b). The apparatus is configured such that the wafer 15 can be transferred to the hand (not shown) by lifting the wafer 15 with the pins 14.
The mirrors 12a and 12b for measuring the positions of the X and Y stages 6 and 7 are extended in the Z direction so that laser light beams emitted from the laser interferometers 11a and 11b are reflected even when the finely adjustable stage 5 lifts or lowers for transferring the wafer. The apparatus is also configured such that the mirrors 12a and 12b do not touch the projection lens 3 even when the X and Y stages 6 and 7 move in the entire operating area.
In the apparatus described above, however, because the mirrors 12a and 12b are placed such that the mirrors 12a and 12b do not touch a lens system and the mirrors 12a and 12b can reflect the lasers emitted from the laser interferometers 11a and 11b for positional measurement even when the finely adjustable mechanism of the finely adjustable stage 5 moves up and down for transferring the wafer, the mirrors 12a and 12b are extended in the Z direction and the finely adjustable mechanism of the finely adjustable stage 5 becomes large in the X and Y directions. Therefore, the apparatus has several drawbacks of having the large finely adjustable stage becoming bulky with a waste of space, requiring a long positioning time due to vibration caused by low rigidity of the finely adjustable stage, and others.